JPS63256043A - Modem for telephone set - Google Patents

Abstract

PURPOSE:To attain sure communication connection without mis-detection of noise by connecting a switch circuit in series with an output terminal of a band pass filter detecting a level of an answer tone and conducting a switch circuit when no network control signal is detected within a prescribed time after the answer tone is detected. CONSTITUTION:A detection signal is outputted from a 1st level detector 10, a one-shot multivibrator 13 is triggered and an output signal rises from a Q output terminal Q1 of the one-shot multivibrator 13 without an output of the detection signal from a 2nd level detector 11 within a prescribed time, 20msec, then a D type flip-flop 14 is latched and an 'H' level is outputted from a Q output terminal Q2 as a carrier detection signal of an 'L' level from the output terminal. Thus, he frequency component of the answer tone 2.1kHz is included and the carrier detection signal is outputted to a reception signal not including only the frequency component in 400Hz of the network control signal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a telephone modem improved so as to be able to reliably detect an answer tone transmitted from a communicating party.

(Prior Art) FIG. 3 is a block circuit diagram of main parts of a conventional telephone modem.

In Fig. 3, 1 is a telephone line connector connected to the telephone line, 2 is a relay for dialing, 3 is an insulating transformer between the telephone line and modem circuit, and 4 is a transmitter for transmitting signals to the telephone line. This is a hybrid circuit that also extracts received signals. And H8 to 1.2 for sending
The carrier wave of 8 is modulated by the transmission data in the modulation circuit 5.
The signal is given to the hybrid circuit 4 as a transmission signal via a transmission bandpass filter 6 whose passband is a frequency band of 00 to 1600Hz. In addition, the hybrid circuit 4
The received signal etc. extracted in is given to a first band pass filter 7 and a second band pass filter 8 for reception. Then, the first bandpass filter 7 has 2 to 2.
The 8KH2 frequency band is used as a passband, and the 2 and 1KH2 answer tones and the 2.4KH2 reception signal sent from the communication partner are extracted from the received signals extracted by the hybrid circuit 4, and the demodulation circuit 9 and the first level detector lO. This demodulation circuit 9 demodulates and outputs the received data from the received signal, and outputs the demodulated data to the first level detector lO.
When it detects that an answer tone has arrived, it outputs a carrier detection signal. Furthermore, the second bandpass filter 8 has a frequency band of 300 to 600H2 as a passband, and the second bandpass filter 8 has a frequency band of 300 to 600H2.
00)12 network control signals are extracted and applied to the second level detector 11. Then, this second level detection 1
When s11 detects that a network control signal has arrived, it outputs a network control signal detection signal.

In such a configuration, the operation when making an automatic call for data communication etc. is explained. First, relay 2 is closed and off-hook, and current flows through the telephone line T, p and R, □.
The voltage between the Then, a 400H2 dial tone, which is a type of network control signal, is sent from the station, and this dial tone passes through the second bandpass filter 8 and is detected by the second level detector 11 to detect the network control signal. A signal is output. By detecting this network control signal, relay 2
is opened and closed to perform dial operations. Then, the station establishes a line connection in accordance with this dial operation and calls the communication partner using a 400 Hz ringback tone, which is a type of network control signal. Then, when the communication partner goes off-hook, the communication partner sends an answer tone of H2 to 2.1, and this answer tone passes through the first bandpass filter 7 and is detected by the first level detector 10. A carrier detection signal is output. Upon detection of this answer tone, a transmission signal is sent to the communication partner, and communication connection control signals and the like are appropriately exchanged to establish a communication connection and data communication becomes possible.

(Problems to be Solved by the Invention) By the way, noise is likely to occur when a line is connected at a station or when a communication partner goes off-hook. The noise generally contains a wide range of frequency components and passes through the first and second bandpass filters 7.8. Then, this noise is erroneously detected as an answer tone, and a communication connection control signal is sent out before the communication partner goes off-hook, causing a problem that communication connection cannot be established. Therefore, the first level detector lO detects that the answer tone is, for example, 50m5ec.
Although it is configured to output a carrier detection signal after continuous detection, it is not always possible to reliably detect only the answer tone.

Furthermore, unless the out-of-band attenuation of the first bandpass filter is set to a large value, the first level detector IO is likely to cause false detection in response to a strong input such as a ringback tone. Therefore, in order to increase the amount of out-of-band attenuation of the first bandpass filter IO, there is a problem that the circuit configuration becomes complicated and expensive.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems of the conventional telephone modem described above, and to provide a telephone modem that can reliably detect answer tones.

(Means for Solving the Problems) In order to achieve this objective, the telephone modem of the present invention has the following features:
a first bandpass filter whose passband is the frequency band of an answer tone sent from a communication partner; and a first level detector that detects the level of the answer tone that has passed through the first bandpass filter. and a second bandpass filter whose passband is the frequency band of the network control signal;
a second level detector that detects the level of the network control signal that has passed through the second band-pass filter, and a switch circuit is connected in series to the output terminal of the first level detector. and the second level detector within a predetermined time after the first level detector outputs the detection signal.
The control circuit is configured to make the switch circuit conductive when no detection signal is output from the level detector.

(Function) Since the switch circuit is connected in series to the output terminal of the first bandpass filter that detects the level of the answer tone,
A carrier detection signal is not output unless this switch circuit becomes conductive. Then, when a detection signal is not output from the second level detector within a predetermined time after a detection signal is output from the first level detector like an answer tone, the switch circuit becomes conductive and a carrier detection signal is output. be done. However, the detection signals are output from the first and second level detectors at the same time like noise, or the detection signals are output from the second level detector within a predetermined time after the detection signals are output from the first level detector. is output, and if a detection signal is output from the first level detector while a detection signal is being output from the second level detector, the switch circuit is not conductive and no carrier detection signal is output.

(Example) Hereinafter, an example of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a block circuit diagram of essential parts of an embodiment of the telephone modem of the present invention, and FIG. 2 is a diagram illustrating the operation of the control circuit of FIG. 1. In FIG. 1, the same reference numerals are given to the same block circuits as in FIG. 3, and the explanation of mFi will be omitted.

? In FIG. 1, the output terminal of the first level detector 10 is connected to the input terminal of an inverter 12 and also to the trigger terminal of a one-shot multivibrator 13. Four output terminals 41 of this one-shot multivibrator 13 are connected to a latch terminal Cp of a D-type flip-flop 14. This D type flip-flop 1
NAND circuit 1 where Q output terminal Q2 of 4 is a switch circuit
The output terminal of the inverter 12 is connected to the other input terminal of the NAND circuit 15. Then, a carrier detection signal is output from the output terminal of the NAND circuit 15. Furthermore, a second level detector 11
The network control signal detection signal is directly outputted from the output terminal of , and this output terminal is connected to the clear input terminal CD of the one-shot multivibrator 13 and the clear input terminal R of the D-type flip-flop 14 . Note that the one-shot multivibrator 13 is, for example, 20m5e.
A pulse of c for a predetermined time is output, and a voltage of +5V is applied to the D input terminal of the D type flip-flop 14.

A control circuit is composed of the one-shot multivibrator 13 and the D-type flip-flop I4.

In such a configuration, the noise includes both the answer tone and the frequency components of the network control signal, as shown in FIG. 2(A).
When detection signals are simultaneously output from the first and second level detectors 10.11, the one-shot multivibrator 13 is triggered but reset at the same time.

Then, when the output signal of the 4 output terminal 4I rises due to the reset of the one-shot multivibrator 13, the +5V voltage applied to the D input terminal of the D type flip 70 tube 14 tries to be latched, but at the same time it is reset and the Q output The terminal Q2 is maintained at the "L" level, the NAND circuit 15 is not conductive, and no carrier detection signal is output. Further, as shown in FIG. 2(B), for example, 2 times within a predetermined time with respect to the output of the detection signal of the first level detector
When a detection signal is output from the second level detector 11 within 0 m5ec, the one-shot multivibrator 13 is first triggered by the detection signal of the first level detector IO, and the detection signal of the second level detector 11 is output. will be reset. Then, at the rise of the output signal of the output terminal ζ due to the reset of the one-shot multivibrator 13, D
The type flip-flop tries to be latched but is reset at the same time and the Q output terminal Q2 is // l, //
The level is maintained, the NAND circuit 15 is not conductive, and no carrier detection signal is output.

Furthermore, as shown in FIG. 2(C), the second level detector 1
If the detection signal of the first level detector IO is output while the first detection signal is output first and continues, the second detection signal is output.
The one-shot multivibrator 13 and the D-type flip-flop 14 are reset by the detection signal of the level detector 11, and the Q output terminal Q2 is
At the l, // level, no carrier detection signal is output.

By the way, if the frequency component of the network control signal is not included, such as an answer tone, the first level detector lO
Even if a detection signal is output from the second level detector 11
No detection signal is output.

Therefore, as shown in FIG. 2(D), the first level detector l
A detection signal is output from O, the one-shot multivibrator 13 is triggered, and the four output terminals of the one-shot multivibrator 13 are output without a detection signal being output from the second level detector 11 within a predetermined time of 20 m5ec. When the output signal of gain and rises, the D type flip-flop 14 is latched and the Q output terminal Q2 becomes
Hn level is output. In this state, the detection signal of the first level detection 310 is also inverted from the inverter 12.
A signal at H level is applied to the NAND circuit 15, and is output from the output terminal as a carrier detection signal at level ll l, //.

Therefore, a carrier detection signal is output only for a received signal in which the answer tone 2.1 contains the H2 frequency component and the network control signal does not contain the 400H2 frequency component.

(Effects of the Invention) As explained above, according to the telephone modem of the present invention, an answer tone can be reliably detected, noise will not be erroneously detected, and communication for data communication etc. can be reliably performed. A connection is made. In addition, since the answer tone and noise are distinguished by detecting the frequency components of the answer tone and the network control signal, the out-of-band attenuation of the first bandpass filter whose pass band is the answer tone frequency band is There is no need to set up the circuit as large as in the case of the above circuit, and the circuit has the excellent effect of being simpler and cheaper to construct.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram of a main part of an embodiment of the telephone modem of the present invention, FIG. 2 is a diagram explaining the operation of the control circuit of FIG. 1, and FIG. FIG. 2 is a block circuit diagram of main parts of a telephone modem. 7: first band pass filter, 8: second band pass filter, lO: first level detector, ll: second level detector, 13: one shot multivibrator, 14: D type flip-flop, 15: Nando circuit. Patent Applicant Alps Electric Co., Ltd. Agent Patent Attorney Tetsuo Moriyama 2nd (A) CB) Figure ((j (D) -11C11

Claims (1)

[Claims] a first bandpass filter whose passband is the frequency band of an answer tone sent from a communication partner; a first level detector that detects the level of the answer tone that has passed through the first bandpass filter; a second bandpass filter whose passband is the frequency band of the network control signal;
a second level detector that detects the level of the network control signal that has passed through the second band-pass filter, and a switch circuit is connected in series to the output terminal of the first level detector. and the second level detector within a predetermined time after the first level detector outputs the detection signal.
1. A telephone modem characterized in that a control circuit is configured to make the switch circuit conductive when no detection signal is output from the level detector.